1. Field of Use
This invention relates generally to an oil separator for separating and collecting oil entrained in a refrigerant circulating through a refrigeration system.
In particular, the invention relates to an oil separator having an improved conduit for injecting a pressurized stream of gaseous refrigerant with oil entrained therein into a lower primary separation section or chamber of the oil separator and for effecting oil separation in the conduit during such injection.
2. Description of the Prior Art
A refrigeration system employs a motor-driven compressor for compressing a gaseous refrigerant which is then supplied in a liquid state to an evaporator wherein the refrigerant re-expands to effect cooling. The refrigerant in a gaseous state is then directed to a condensor from which it is returned to the compressor for recirculation. The compressor, whether it is a piston-type or a screw-type, requires that oil be supplied thereto to effect sealing of clearance spaces between movable compressor components and enable proper compressor operation. Screw-type compressors, which typically employ two intermeshed spiral rotors, require substantially more oil than piston-type compressors. In any case, some of the oil supplied to the compressor becomes entrained in the refrigerant flowing through the system, either in the form of oil vapor or oil droplets or both, and must be removed to ensure proper system operation by means of an oil separator added to the system. The oil so removed is re-used by the compressor. Oil in the system is undesirable because it coats the inner walls of the system piping and reduces heat transfer in critical areas; it accummulates and clogs refrigerant flow paths; and a foamy mixture of refrigerant and oil, especially in screw compressor systems, interferes with the proper refrigerant flow and behavior.
One type of prior art oil separator comprises a vessel having a chamber therein which is divided into a lower primary oil separation section or chamber and an upper secondary oil separation section or chamber by oil coalescing separator means which include a horizontal plate. The plate contains one or more holes therethrough and an oil coalescing separator element is fitted over each hole in the upper section of the chamber. The vessel is provided with a gas outlet port communicating with the upper section and with an oil outlet port communicating with an oil sump in the bottom of the lower section.
Referring to FIGS. 5, 6 and 7 herein labelled "PRIOR ART", gaseous refrigerant with oil entrained therein (hereinafter sometimes called a "mixture") is introduced under pressure through a mixture inlet pipe A which extends through the side wall of the vessel B into the lower primary section. The mixture inlet pipe has a mixture inlet opening C exteriorly of the vessel and a discharge opening D located in the lower primary section adjacent an inner surface of the side wall of the vessel. The mixture inlet pipe has a horizontally disposed S-shaped passage E (FIG. 7) therethrough which acts upon the mixture flowing therethrough so as to separate oil mist and oil droplets H from the gaseous refrigerant under centrifugal force as the mixture negotitates each of the two curves F and G in the passage. The oil mist and droplets H impinge and collect on the outermost passage wall surface of each curve F and G, flow out of discharge opening D onto the inner surface of the side wall of vessel B under the force of gas flow exiting the discharge opening and drain down by gravity into the oil sump. During transit of the mixture through the S-shaped passage E, a substantial proportion of oil is removed from the refrigerant. Residual oil in the refrigerant is subsequently removed by the oil coalescing separator elements as the gaseous refrigerant passes therethrough from the lower primary section into the upper secondary section and then drains or drips down from the holes in the plate into the sump. The gaseous, substantially oil-free refrigerant then exits from the upper section through the gas outlet port is returned to the condenser. Oil is withdrawn from the sump through the lower oil outlet port for re-use in the compressor.
As is apparent from the foregoing description of the prior art oil separator, the mixture of gas and oil enters through mixture inlet pipe A whose passage E has a complex S-shaped curve and effects oil separation by reliance on centrifugal force acting on the oil mist as the mixture changes direction. Upon exiting the curved passage E and entering the lower primary section, the velocity of the gas (with residual oil therein) drops appreciably, and there is a sudden direction change as the gas stream impinges on the inner surface of the side wall of vessel B. The centrifugal action, velocity reduction, and direction change forces more that 90% of the oil to drop out and collect in the oil reservoir. The residual oil, flowing along with the gas, is almost completely removed by the coalescing elements in the upper section of the separator.
It has been discovered that the oil separation efficiency of the prior art oil separator is less than ideal due to the shape and disposition of the mixture inlet pipe A. In particular, some oil separated in S-shaped passage E is re-entrained into the mixture before exiting the passage E. As FIG. 7 shows, some of the oil mist and droplets H that separated at the first curve F in S-shaped passage E and collected on the outer side of the first curve F are flung transversely across the high-velocity gas stream flowing through the passage and re-enter the gas stream and, along with oil still in the stream, again need to be separated at the second curve G in the S-shaped passage E and collected on the outer side of the second curve G. As larger and larger oil droplets form at the first curve F, there is a tendency for some of the oil droplets H to re-entrain while the oil is passing at right angles to the gas. The re-entrained oil, in large droplets, as well as some oil mist not removed at the first curve E, passes on to the outer side of the second curve G where it separates from the gas stream and collects. The fact that not all oil particles H which have re-entered the stream are recovered at the second curve G, results in inefficient oil recovery.